In recent years, development of a facial recognition technique for recognizing a face from a captured still image or moving image has progressed. In a vehicle, an apparatus has been devised in which inattentive driving or dozing off while driving is detected by detecting blinking operation of an operator, and warning is given to the operator.
For example, an apparatus disclosed in JP 2000-040148A (Reference 1) sequentially captures images including a left eye region (window) of a driver, determines regions in which a luminance difference between the images exceeds a predetermined value through comparison between the latest image and the previous image, and calculates an area difference between a region whose luminance increases and a region whose luminance decreases. The time series data is compared with a predetermined blinking pattern so that a blinking operation of the driver is extracted, and thus treatment for preventing dozing while driving is performed. In other words, this apparatus detects the blinking operation with a region of a single eye as a reference. Therefore, if the face moves, a position and a shape of the eye changes, and thus the region used as a reference of detection also changes. For this reason, it is difficult to accurately identify the region used as a reference for detection, and thus errors in detection of a blinking operation frequently occur.
In addition, an eyelid detection apparatus disclosed in US 2008/0212850 (Reference 2) extracts a region in which an area of a region (difference region) where a difference between captured images exceeds a predetermined value is at maximum, detects an eyelid in the difference region, and further detects a blinking operation from a variation in the eyelid. This apparatus extracts a rectangular region which is in contact with a driver's face from the image, and identifies a difference region between a plurality of images of the region so as to detect a blinking operation. In other words, a region which is compared in order to detect a blinking operation is set with a contour of a face as a reference.
Here, in a case where the driver confirms directions of the vehicle with rearview mirrors, an angle of the face varies in a yaw direction or the like with respect to a vehicle traveling direction. For this reason, the shape and size of the rectangular region which is a detection target of a blinking operation vary, and thus difference regions also occur in the nose, eyebrows, face perimeter, and the like which are regions other than the eyes. If a difference region in which an area variation is the maximum is a region other than the eyes, the region other than the eyes, for example, the face perimeters, the eyebrows, or the like are wrongly detected as the eyes. In other words, in the apparatus disclosed in Reference 2, since a region for detecting the eyelids is set with a contour of the face as a reference, detection errors tend to occur if the contour of the face significantly changes.
As mentioned above, in the apparatuses of the related art, in a case where a driver's face moves, detection errors occur.
As described above, in the apparatus disclosed in Reference 1, since a blinking operation is detected on the basis of a region of only one eye, the region for detection varies due to the movement of the entire face, and thus errors in detection of a blinking operation tend to occur. In addition, in the apparatus disclosed in Reference 2, since the region for detecting the eyelids is set with the contour of the face as a reference, similarly, detection errors tend to occur due to the movement of the entire face.